The use of drop axles in vehicles, particularly trucks, has been well-known in the trucking industry for many years. The use of these drop axles provides various, known, commercial and safety advantages. They are, therefore, often installed for one or more of these purposes (or simply as a matter of choice) on light, medium, and heavy-duty trucks.
One advantage is that by dropping the center portion of an axle (i.e., relative to the axle ends), it is possible to extend the drive shaft of a vehicle without the drive shaft interfering with the center beam portion of the axle (thereby allowing direct drive, for example), which interference often times prohibits use of the suspension in this position, e.g., sometimes referred to as the “pusher” position.
As an additional important advantage of such axle configurations, such as in vehicles employing lift-type suspensions, the drop axle provides increased clearance (as compared to a straight axle) between the vehicle frame and the axle beam. This, then, as one advantage, allows for a larger air spring to be employed. As another advantage, this larger clearance space and air spring, in turn, permits the axle to be lifted a greater distance from the road surface which is a distinct advantage, particularly in off-road conditions where ground obstructions may be encountered. Moreover, the use of these drop axles provides for a generally more stable (e.g., generally less top heavy) ride due to its reduced ride height.
An example of a particularly successful, known, lift axle suspension system which employs a drop axle in combination with a lift-type suspension is disclosed in U.S. Pat. No. 5,810,377, entitled FABRICATED STEER AXLE. This patent is commonly assigned and has an overlapping inventorship entity herewith.
Although known lift axles, such as described in the '377 patent, provided various useful commercial and functional utilities, they had certain known economic limitations or drawbacks. In this regard, such drawbacks often related to the highway weight limit laws which are imposed in order to limit the permissible maximum load of a vehicle when used on a highway (and thereby limit the profit realized from the amount of cargo that is carried) as a function of the number of its axles. Taking into account such laws, minimizing the weight of axle and/or suspension systems is highly desirable and results in increased operational profitability. In certain embodiments, this invention achieves this desirable result.
Typical full (or partial) drop axles that were heretofore used, exhibited abrupt curves or angles at or near the junction of the two axle ends where they meet the middle beam portion of the axle, thus, to form the “drop” portion of the axle. In particular, these structural changes have been conventionally employed in order to achieve the desired differential between the height of the axle ends relative to the height of the middle beam portion (e.g., as measured from ground level when installed on a truck). In some exemplar embodiments of such prior art axles, the angles at such junctions frequently range from approximately 20-50 degrees and, in some cases, actually approached 90 degrees.
Unfortunately, manufacturing such abrupt or sudden angle changes into the axle beams has been found to introduce stress risers along the length of the beam which can potentially weaken the axle (e.g., in part, as a result of the manufacturing process which involves heating and bending the axle to achieve the desired angle change).
This, in turn, can reduce the axle's strength to weight ratio or, in other instances, necessitate structural changes which themselves can cause significant, detrimental stress risers to occur. In order, then, to ensure that a given prior art axle had sufficient strength, very thick axle tube walls (or solid, non-tubular axles) were characteristically employed. This undesirably increased the weight of the axle and, thus, reduced the cargo limit that could be lawfully carried.
In view of the above problems in the art, there existed a need in the art, prior to this invention, for an axle and, optionally, a spindle assembly, as well as a combination thereof, which would overcome these problems or, at least, mitigate them. It is a purpose of this invention to fulfill this need in the art, as well as other needs which will become apparent to the skilled artisan once given the above disclosure.